Thin-film technology is widely used for performance improvement and size reduction of devices. Thin-film devices not only provide direct benefits to users, but also play an important role in environmental aspects, such as in protection of earth resources and in reduction of power consumption.
A film formation technique that allows a high deposition rate is essential in order to increase the productivity of thin films. Increase in deposition rate is being pursued in film formation methods such as vacuum evaporation methods, sputtering methods, ion plating methods, and CVD methods (Chemical Vapor Deposition Methods). A take-up type thin film production method is known as a method for continuously producing thin films in large numbers. In the take-up type thin film production method, an elongated substrate is unwound from an unwinding roll, a thin film is formed on the substrate being conveyed along a conveyance system, and the substrate is then wound on a winding roll. For example, thin films can be formed with good productivity by combining the take-up type thin film production method with a film formation source that allows a high deposition rate, such as a vacuum evaporation source using electron beam.
Factors that determine success and failure of such a continuous take-up type thin film production include thermal load during film formation, and cooling of the substrate. For example, in the case of vacuum evaporation, thermal radiation from an evaporation source and thermal energy of evaporated atoms are applied to a substrate, and the temperature of the substrate is thus increased. Also in other film formation methods, although the heat source is different, thermal load is applied to a substrate during film formation. The substrate is cooled in order to prevent, for example, deformation and meltdown of the substrate from occurring due to such thermal load. The cooling is not necessarily carried out during film formation, and may be carried out in a region of a substrate-conveyance route other than the film formation region.
As means for cooling a slurry or the like with a roller in the atmosphere, Patent Literature 1 discloses a cooling roller including: a cylindrical body whose wall is provided with a plurality of slits or holes; and a partition plate provided in the cylindrical body. The cylindrical body can rotate relative to the partition plate in a sliding manner, and a coolant gas emitting pipe is provided in a space defined by the partition plate. With this cooling roller, a slurry can be sprayed with a large amount of the coolant gas, and thus can be cooled by removing heat directly from the slurry.
However, in a vacuum atmosphere, such a large amount of coolant gas as to allow direct removal of heat cannot be used in view of maintaining the vacuum. As an example of methods for cooling a substrate during film formation, there is a widely-used method in which a film is formed on a substrate extending along a cylindrical can disposed on a conveyance route of a conveyance system. With this method, heat can be released to a cooling can of large heat capacity by ensuring thermal contact between the substrate and the cylindrical can. Thus, increase in the temperature of the substrate can be prevented. In addition, the temperature of the substrate can be maintained at a specific cooling temperature. Cooling of the substrate by a cooling can is effective also in a region of the substrate-conveyance route other than the film formation region.
One of the methods for ensuring thermal contact between a substrate and a cylindrical can is a gas cooling method. Patent Literature 2 teaches that, in an apparatus for forming a thin film on a web serving as a substrate, a gas is introduced into a region between the web and supporting means. With this method, heat conduction between the web and the supporting means can be ensured, and thus increase in the temperature of the web can be suppressed.
In addition, a cooling belt can also be used as means for cooling a substrate, instead of the cylindrical can. When carrying out film formation using obliquely incident components, it is advantageous, in view of material use efficiency, to form a film on a substrate traveling linearly. In that case, the use of a cooling belt as means for cooling the substrate is effective. Patent Literature 3 discloses a method for cooling a belt used for conveyance and cooling of a substrate material. According to the method disclosed in Patent Literature 3, in the case where a cooling belt for improving the efficiency of thin film formation is used in a thin film formation apparatus that causes thermal load, a cooling mechanism using two or more other cooling belts or a liquid medium is provided inside the cooling belt in order to cool the cooling belt itself. This can increase the cooling efficiency, and thus can lead to improvement of the characteristics of a magnetic tape such as electromagnetic conversion characteristics, and also to significant improvement of the productivity.
Patent Literature 4 describes a substrate-conveying roller that causes less damage to a substrate and that allows gas cooling while preventing deterioration in the degree of vacuum.